Site grading: surface drainage diverted away from foundation; 6 in fall in first 10 ft
2025 RCNYS §R401.3 Surface drainageDescription
Surface drainage must be diverted to a storm-sewer conveyance or other approved point of collection that does not create a hazard. Lots must be graded to drain surface water away from foundation walls — typical guidance is a fall of at least 6 in in the first 10 ft (5% slope). Where lot lines or other physical conditions prohibit this slope, the water must be diverted by drains or other approved methods.
Why this exists
Surface water at the foundation is the leading cause of basement moisture problems. The 6-in / 10-ft fall is the architect's responsibility on the site plan — easy to specify, expensive to retrofit. Roof leaders should discharge at least 5-10 ft from the foundation as well, not directly to grade.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
fallFirst10 | min | 6 | in over 10 ft (5%) | Typical site fall away from foundation |
Categories
Applies to
- Jurisdiction: New York State
Source
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Habitable space minimum ceiling height · IRC R305.1
- Wind design · IRC R301.2.1
- Seismic provisions · IRC R301.2.2
- Snow loads · IRC R301.2.3
- Floodplain construction · IRC R301.2.4
Last reviewed 2026-05-15.